Method and device for distinguishing among a plurality of devices and data elements with a sequence of signals

ABSTRACT

A method and device for decoding a sequence of signals in which information is derived, in part, from a duration of (a) one of the signals and/or (b) an inter-signal pause between two of the signals. The method and device may also be used to decode a signal to form decoded information, derived, in part, from a duration of the signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.08/720,124, filed Sep. 27, 1996.

FIELD OF THE INVENTION

The present invention relates to the decoding of a sequence of signals.In particular, the present invention relates to the communication ofsignaling information, such as dual tone multiple frequency (or “DTMF”)signals, across a telecommunications network, for example, the publicswitched telephone network, and the receipt and decoding (orinterpretation) of such signaling information.

BACKGROUND OF THE INVENTION

In telecommunications systems, signaling performs three basic functions;namely (1) supervising functions, (2) alerting functions, and (3)addressing functions. Signaling for supervising functions is used tomonitor the status of a transmission line or circuit to determine thestate of the line or circuit (i.e., whether it is busy, idle, requestingservice, etc.). Voltage levels, tone or data bits for example, are usedfor supervising function signals. Signaling for alerting functions isused, for example, to indicate the arrival of an incoming call withe.g., bells, buzzers, tones, strobes, lights, etc. Signaling foraddressing functions is used to route signals over the network with, forexample, dial pulses, tone pulses, and data packets.

Today, most signaling is carried out “in-band” (i.e., it goes along withvoice conversations, and occupies the same circuits as those which carryvoice conversations). Such in-band signaling is usually carried out withmulti-frequency or single frequency signals. Unfortunately, many tollcalls are not completed because the called telephone (or otherequipment) does not pick up or is busy. Consequently, the circuit timeused in signaling, which is substantial and expensive, becomes wasteful.Out-of-band signaling (such as signaling system 7, or “SS7”) usescircuit(s) separate from voice circuits for signaling functions.

Although one skilled in the art understands the station equipment andtransmission facilities used by Regional Bell Operating Companies (or“RBOCs”), a brief overview of such station equipment and transmissionfacilities is provided below for the reader's convenience.

FIG. 1 illustrates the use of transmission facilities by various typesof services. As shown in FIG. 1, a number of geographically remotecentral switching offices 120 are coupled via “trunks” 114 andinteroffice transmission facilities 118. Various entities, such asresidences 102, businesses 104, and private branch exchanges (or “PBXs”)106 are coupled with a central switching office 120 via “lines” 110, 112and “loop transmission facilities” 108.

Thus, a loop transmission facility (or “subscriber loop”) 108 connectstelecommunication equipment at a customer premises (e.g., a residence,business, etc.) with an associated central switching office 120. Theloop transmission facility 108 is typically on the order of a few milesand usually includes paired copper wire. Interoffice transmissionfacilities 118, or trunks, connect different central switching offices120. Interoffice transmission facilities 118 range from less than onemile to thousands of miles.

FIG. 2 is a block diagram showing the connection of two pieces ofterminal equipment at customer premises served by separate centraloffices. Terminal equipment X 202 (such as a telephone or modem forexample) is coupled with central office A 206, via loop 208. Similarly,terminal equipment Y 204 is coupled with central office B 210, via loop212. Central office A 206 is coupled with central office B 210 via trunklines 214. If all of the trunk lines 214 are busy, central offices A andB, 206 and 210, respectively, may be coupled via trunks 216 and 220 andtandem office C 218.

The flow diagram of FIGS. 3a through 3 d illustrates steps involved withinitiating a call from terminal equipment X 202 to terminal equipment Y204, processing the call, and terminating the call, in a system using“in-band” signaling. For the purposes of the following discussion, itwill be assumed that the terminal equipment X 202 and Y 204 aretelephones. However, the terminal equipment X 202 and Y 204 may be othertypes of equipment, such as a modem for example.

FIG. 3a shows actions taken at the telephone X 202 and the centraloffice A 206 in initiating the call. First, as shown step 302, when thehandset of telephone 202 is lifted, it sends an off-hook signal to thecentral office A 206 via loop 208. At central office A 206, a changefrom on-hook to off-hook status is detected. More specifically, when thetelephone X 202 is taken off-hook, a circuit is established and thecentral office A 206 detects a DC current flowing through theestablished circuit. As shown in step 304, this change in status isinterpreted as a request for service. Next, as shown in step 306,assuming that an originating register is available to accept and storethe digits to be dialed by telephone X 202, the central office A 206connects a dial tone signal to the telephone X 202 via loop 208. Lineside equipment, such as an analog line unit (or “ALU”) or an integrateddigital carrier unit (or “IDCU”) for example, provides the dial tonesignal. As shown in step 308 a number is then dialed at telephone X 202.In response, as shown in steps 310 and 312, once the first digit of thenumber is recognized, the dial tone is disconnected and the numbers arestored in the originating register.

FIG. 3b shows actions taken at the central office A 206 in processingthe call. First, as shown in step 314, control equipment at centraloffice A 206 translates the dialed number. The control equipmentperforms this translation with a dual tone multiple frequency decoder(or DTMF) receiver which is discussed in more detail below. As shown instep 316, by examining the leading digits (e.g., the first three digits)of the dialed number, the control equipment determines whether the callis to another central office (i.e., an “inter-office” call) or to asubscriber serviced by the same central office (i.e., an intra-officecall). In this example, it is assumed that the call is to telephone Y204 which is served by a separate central office; namely, central officeB 210. Next, as shown in step 318, routing information stored in thesystem indicates which paths (or “trunk groups”) are appropriate andtranslates the desired paths to representations of physical locations ofterminations of the trunks. As shown in step 320, if the call isbillable, an automatic message accounting (or “AMA”) register isrequested to enable the telephone service provider to bill theappropriate parties. Next, as shown in step 322, the call information istransferred to an outpulsing register and the originating register isreleased. Then, as shown in step 324, the control equipment at centraloffice A 206 begins scanning outgoing trunks to find an idle trunk tocentral office B 210.

If an idle trunk is found, as indicated in step 326, the call betransmitted directly from central office A 206 to central office B 210via a free trunk 214. If, on the other hand, all trunks 214 from centraloffice A 206 to central office B 210 are busy, then outgoing trunks 216to tandem switching office C 218 are scanned such that the call may berouted from central office A 206 to central office B 210 via tandemswitching office C 218.

FIG. 3c illustrates the actions taken to advance the call to theterminating central office; namely central office B 210. First, as shownin step 328, the idle trunk found in step 326 is seized. In response, asshown in steps 330 and 336, at central office B 210, an incomingregister of a switch is seized and control equipment sends a readysignal back to central office A to indicate that the seized incomingregister is ready to receive address information. In the meantime, asshown in step 332, at central office A 206, the line of telephone X 202is connected, via the loop 208 and a switching network within centraloffice A 206, to the seized trunk. In addition, as shown in step 334,control equipment at central office A 206 scans the outgoing trunk forthe ready signal.

As shown in steps 338 and 340, when the ready signal sent by centraloffice B 210 is received and detected by central office A 206, the callinformation is communicated from the outpulsing register of centraloffice A to the seized incoming register of central office B 210. Next,as shown in step 342, before the last digit of the dialed number issent, the control equipment at central office A 206 checks to see iftelephone X 202 is still off-hook. If telephone X 202 is on-hook, thecall is abandoned and the control equipment at central office A willterminate the call processing sequence and release associated equipmentand circuits (e.g., seized registers, trunks, etc.). If, on the otherhand, telephone X 202 is still off-hook, as shown in steps 344 and 346,the last digit of the dialed number is transmitted from the outpulsingregister of central office A206 to the incoming register at centraloffice B 210 and the outpulsing register of central office A 206 isreleased.

FIG. 3d illustrates the actions taken to complete the call. First, asshown in step 350, the digits of the called number stored in theincoming register of the central office B 210 are translated to aphysical location of the termination of the loop 212 of telephone Y 204at central office B 210. Next, as shown in step 352, the status of theloop 212 of telephone Y 204 is checked to determine whether it is idleor busy. If the loop 212 is busy (i.e., telephone Y 204 is off-hook), abusy signal is returned to telephone X 202 via the switching network ofcentral office B 210, trunk 214, the switching network of central officeA 206, and loop 208. However, for purposes of this example, it isassumed that the loop 212 of the telephone Y 204 is idle (i.e.,telephone Y is on-hook). In such a case, the incoming trunk 214 iscoupled with the loop 212 of telephone Y 204 via the switching networkof central office B 210. Next, as shown in steps 356, 358, and 360, aringing register in central office B 210 is seized, the incomingregister which stored the dialed number is released, and a ring signalis enabled. The ring is generated by the control equipment. As shown insteps 362 and 364, the ring signal causes an audible ring to betransmitted to telephone X 202 (via the switching network of centraloffice B 210, trunk 214, the switching network of central office A 206,and loop 208) and causes telephone Y 204 to ring (via loop 212). Controlequipment at central office B 210 monitors the status of the telephone Y204. If the handset of the telephone Y 204 is taken off-hook (see step366) the ringing signal is disabled. The conversation then begins.Further, as shown in step 368, answer supervision, used to record answeror connect time for billable calls, is provided by control equipment atcentral office A 206.

As shown in step 370, control equipment at central office A 206 monitorsthe outgoing trunk 214 for disconnect. The call is terminated if eithertelephone X 202 or telephone Y 204 is hung up, i.e., if its handset isplaced on-hook. If the calling party, i.e., telephone X 202, hangs upfirst, the connection is released (see step 374), and disconnectsupervision is sent to central office B 210. The trunk is then idledwhen central office B returns on-hook supervision. If, on the otherhand, the called party, i.e., telephone Y 204, hangs up first, a timedrelease period of 10 to 11 seconds is initiated. Finally, as shown insteps 372 and 374, upon the expiration of this timed release period, theconnection is released.

The above example describes an inter-office call. An intra-office callis handled similarly except that an idle trunk line is not needed.Basically, for intra-office calls, steps 314, 316, 318, 320, 322, 324,326, 328, 330, 332, 334, 336, 338, 342, 344, and 346 are not performed.Moreover, steps 350, 352, 354, 356, 358, 360, 364, 366, and 372 are allperformed at central office A.

To reiterate, the above described flow diagram of FIGS. 3a through 3 dillustrates the steps involved with initiating a call from terminalequipment X 202 to terminal equipment Y 204, processing the call, andterminating the call, in a system using “in-band” signaling. Manypresent day inter-office networks now use out-of-band signaling such asSS7 signaling to “set up” (or establish) and “tear down” (or terminate)a call. SS7 is used to send messages between remote switching equipment.SS7 is advantageous because it uses separate circuits for signaling andvoice data. To reiterate, in the previous systems, the same circuit wasused for both signaling and voice data. Such previous systems weredisadvantageous because if a circuit was being used for signaling, itcould not be used for voice. On the other hand, with SS7, voice trunksare only used when a connection is established.

FIG. 4 illustrates the process of setting up (or establishing) a call400 in a communications system using SS7. First, as shown in step 402, acaller goes off-hook. Again, the off-hook status of the loop is assumedby the central office based on a DC current through the loop, and thecentral office returns a dial tone signal to the caller. Next, as shownin step 404, the caller dials digits which causes pulses or DTMF signalsto be sent to the central office.

For the purposes of describing the present invention, it will be assumedthat the dialed digits will be represented by DTMF signals. As shown inFIG. 5, Each of the digits 0 through 9, as well as the star 11*11 the anthe pound sign “#”, are represented by a pairing of one of four (4) lowfrequencies (697, 770, 852, or 941 Hz) with one of three (3) highfrequencies (1209, 1336, or 1477 Hz). Since such signaling is “in-band”,and since the frequencies are within the range of human voice, thedigits are represented by a paired low and high frequency to avoidhaving the human voice inadvertently imitating or “falsing” one of theDTMF signals. The amplitudes of the low frequency and high frequencycomponents of the dual tone are also compared with a threshold(s) andeach other, to further reduce the chance of falsing.

Next, as shown in step 406, the dialed digits are received and decodedby equipment at the central office. Such equipment may include astandard DTMF decoder such as a model M-8870 DTMF Receiver sold byTeltone. Typically, a DTMF receiver will convert valid dual tones—i.e.,dual tones that: (i) meet a minimum amplitude requirement; (ii) meet aminimum duration requirement (e.g., 18 ms); and (iii) have a minimuminterdigit pause (e.g., 18 ms). However, the amplitude, duration andinterdigit pauses are not themselves interpreted as carrying anyinformation—they are only used to determine whether or not a signal isvalid.

Next, as shown in step 408, if available, a signaling trunk to thedestination office is seized based on a routing table and the decodeddialed digits. As shown in steps 410, 412, and 414, if the dialedequipment is off-hook (i.e., if the line is busy), (i) the destinationoffice signals the central office that the line is busy and (ii) thecentral office provides busy signal tones to the caller. On the otherhand, as shown in steps 410, 416, and 418, if the dialed equipment isnot off-hook, (i) the destination office provides ring to the calledequipment, (ii) the destination office signals the central office thatthe line is free, and (iii) the central office provides a ring signal tothe caller.

Next, as shown in steps 420 and 422, if the called equipment has goneoff-hook, i.e., if the called equipment answers the ring, a connectionis established; that is, a voice circuit is seized. If, on the otherhand, the called equipment has not gone off-hook, the ringing continuesuntil the attempted call is terminated (not shown) or until the calledequipment goes off-hook.

The limited ways of interpreting the twelve dual tone signals limits theinformation which can be conveyed by a sequence of fixed size (e.g.,seven (7) dual tones or ten (10) dual tones). This inherently causes anumber of problems, some of which may be classified as line distinctionproblems, and some of which may be classified as convenience problems.

Regarding the line distinction type problems, as the number of linesused continues to increasing, due to, for example, the increasingprevalence of facsimile machines, modems, home office lines, pagers,etc., area codes are being reformatted. This is disadvantageous becausepeople must remember new area codes and private equipment must bereconfigured to work with the new area codes. For example, some privateequipment cannot handle new three (3) digit office codes of the formatNNX, where N is a number from 2 to 9 and X is a number from 0 to 9. Suchprivate equipment can only recognize three (3) digit office codes of theformat XZX, were Z is either 0 or 1. A similar problem has happened withthe limited number of toll-free “800” numbers—now, “888” is also beingused for toll-free numbers. Some private equipment will not recognize888 as a toll-free number.

Regarding the convenience problems, as the use of facsimile machines,e-mail, modems, pagers, etc. continues to increase, it will becomeincreasingly difficult for people to remember and recall all of thosenumbers. Although automated touch tone menuing and call forwardingsystems have alleviated this problem somewhat, such systems arerelatively expensive and require set up time by each end user. Anotherconvenience problem concerns the use of dual tones to enter a securitycode. On the one hand, if the number of digits entered is too small, thesecurity code would not offer much security and unauthorized access willbe made easier. On the other hand, if the number of digits entered istoo large, the security code will be difficult to remember therebypossibly preventing authorized people from access or causing authorizedpeople to write down their security number, which may then be lost,copied or stolen. Finally, certain services, such as TeleBroker byCharles Schwab & Co., Inc., require users to “type” letters with theirtelephone keypad. To “type” a letter, (i) the keypad number to which theletter is assigned is pressed, and (ii) the position of the letter onthat number (i.e., first, second, or third) is pressed. FIG. 10 shows adouble digit entry to letter conversion table. Unfortunately, such asystem requires two entries per letter.

In view of the above, a method and device for interpreting additionalinformation from a sequence of signals, such as dual tone signals forexample, is needed.

SUMMARY OF THE INVENTION

The present invention obviates the aforementioned problems by providinga method for decoding a sequence of signals to form decoded information.The method (a) determines information from an inherent property of eachof the signals of the sequence, (b) determines additional informationfrom a duration of one of the signals and/or an inter-signal pausebetween two of the signals, and (c) combines the information determinedin step (a) and the additional information determined in step (b) toform the decoded information. Each of the signals may be a dual tonesignal and the inherent property of each of the signals may be a highand low frequency pair of the dual tone signal. The sequence of signalsmay be an entered seven digit number.

A central office may use the method of the present invention to route acall based on the decoded information. The call may be routed to aperson's telephone, facsimile, pager, e-mail, voice mail, etc.

The step of determining additional information may be based on aduration of each of at least two, at least three, at least four, atleast five, at least six, or all of the signals. Alternatively, the stepof determining additional information may be based on durations ofinter-signal pauses between three of the signals, four of the signals,or each of the signals.

The present invention also provides a device for decoding a sequence ofsignals to form decoded information. The device includes (a) a firstunit that determines information from an inherent property of each ofthe signals of the sequence, (b) a second unit that determinesadditional information from a duration of one of the signals and/or aninter-signal pause between two of the signals, and (c) a combiner thatcombines the information determined by the first unit and the additionalinformation determined by the second unit to form the decodedinformation. The first unit may be a dual tone multiple frequencydecoder. The second unit may include a timer for determining theduration, and a duration-to-state translator that determines theadditional information from the duration.

The method may also be used to decode a signal to form decodedinformation by (a) determining information from an inherent property ofthe signal, (b) determining additional information from a duration ofthe signal, and (c) combining the information determined in step (a) andthe additional information determined in step (b) to form the decodedinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to thefollowing description of an exemplary embodiment thereof, and to theaccompanying drawings, wherein:

FIG. 1 illustrates the use of transmission facilities by various typesof services;

FIG. 2 is a block diagram showing the connection of two pieces ofterminal equipment at customer premises served by separate centraloffices;

FIGS. 3a through 3 d depict a flow diagram which illustrates stepsinvolved with initiating a call, processing the call, and terminatingthe call, in a system using “in-band” signaling;

FIG. 4 is a flow diagram which illustrates the steps involved in settingup a call in a system using “out-of-band” signaling such as SS7;

FIG. 5 is a table showing the low and high frequency pairs used torepresent digits with dual tone signals;

FIG. 6 illustrates two examples of using signal duration to inferinformation;

FIG. 7 is a table which compares the information which may be conveyedwhen one or more of the up to a sequence of seven (7) digits representsthree (3) states in accordance with the present invention, withconventional dual tone multiple frequency (DTMF) receivers;

FIG. 8 is a table which compares the information which may be conveyedwhen one or more of the up to a sequence of seven (7) digits representstwo (2) states in accordance with the present invention, withconventional dual tone multiple frequency (DTMF) receivers;

FIG. 9 is a block diagram of a decoder of the present invention;

FIG. 10 is a double digit entry to letter conversion table used todecode letters “typed” on a telephone keypad; and

FIG. 11 is an ASCII conversion chart.

DETAILED DESCRIPTION

The present invention interprets the duration of, and/or the duration ofthe pause between, signals, such as dual tone signals, as additionalinformation. FIG. 6 illustrates two (2) examples of how the duration ofthe dual tones may be interpreted as additional information. Inconventional telephone DTMF receivers, a given tone pair represents agiven digit—nothing more. For example, as shown in FIG. 5, 770 Hz and1336 Hz dual tone is interpreted as representing the digit “5”. FIG. 6is a timing diagram which illustrates how a given dual tone signal canbe interpreted differently depending on its duration.

As shown in FIG. 6, a first grouping of tone durations 602 exemplifieshow a given tone pair (e.g., 770 Hz and 1336 Hz) can represent one ofthree possible states based on its duration. As shown in FIG. 6, underthe example illustrated in group 602, if the tone pair 604 a has aduration of between 18 ms and 500 ms, it represents a first state. Thedetection device of the present invention may generate a bit pair (e.g.,00) in addition to the information derived from the tone frequencies andshown in FIG. 5. If the tone pair 604 b has a duration of more than 500ms and up to one (1) second, it represents a second state and the deviceof the present invention may generate a bit pair (e.g., 01) in additionto the information derived from the tone frequencies. Finally, if thetone pair 604 c has a duration of more than one second, it represents athird state and the device of the present invention may generate a bitpair (e.g., 10) in addition to the information derived from the tonefrequencies.

FIG. 7 is a table which compares the information which may be conveyedwhen one or more of a sequence of seven (7) digits represents threestates in accordance with the present invention, with conventional dualtone multiple frequency (DTMF) receivers. As shown, in a conventionalsystem, a sequence of (7) digits, each having one of ten (10) possiblestates (based on the low and high frequency pair) has 10,000,000 (or10⁷) possible states. As FIG. 7 shows, this number of possible states istripled for every digit of the seven (7) digits that have 30 possiblestates (based on the low and high frequency pair and based on theduration of the paired frequencies).

A second grouping of tone durations 650 exemplifies how a given tonepair (e.g., 770 Hz and 1336 Hz) can represent one of two possible statesbased on its duration. As shown in FIG. 6, under the example illustratedin group 650, if the tone pair 652 a has a duration of between 18 ms andone (1) second, it represents a first state. The device of the presentinvention may generate a bit (e.g., 0) in addition to the informationderived from the tone frequencies. If the tone pair 652 b has a durationof more than one (1) second, it represents second state and the deviceof the present invention may generate a bit (e.g., 1) in addition to theinformation derived from the tone frequencies.

FIG. 8 is a table which compares the information which may be conveyedwhen one or more of the sequence of seven (7) digits represents two (2)states in accordance with the present invention, with conventional dualtone multiple frequency (DTMF) receivers. As shown, in a conventionalsystem, a sequence of (7) digits, each having one of ten (10) possiblestates (based on the low and high frequency pair) has 10,000,000 (or10⁷) possible states. As FIG. 8 shows, this number of possible states isdoubled for every digit of the seven (7) digits that have 20 possiblestates (based on the low and high frequency pair and based on theduration of the paired frequencies).

As will be apparent to those skilled in the art, the selection of statesfrom among a number of duration ranges may vary. However, human factors,such as the ability of people to accurately and precisely predict timeranges should be considered when determining which durational rangeswill represent which states and the number of states used.

The duration of pauses between pressing digits may also be used toconvey information in a similar manner. Again, human factors should beconsidered.

FIG. 9 is a block schematic of an exemplary decoder of the presentinvention. As shown in FIG. 9, a high frequency detection unit 902 isused to detect the presence of the high frequencies listed in the tableof FIG. 5 (i.e., 1209 Hz, 1336 Hz, 1477 Hz, and 1633 Hz) and a lowfrequency detection unit 914 is used to detect the presence of the lowfrequencies listed in the table of FIG. 5 (i.e., 697 Hz, 770 Hz, 852 Hz,and 941 Hz). The high and low pass filters 904 and 916, respectively,serve to split the band of the incoming frequencies. The outputs of highand low group filters 906 and 918, respectively, are provided, viacomparitors 908 and 920, respectively, to a DTMF encoder 912. The DTMFencoder 912 provides a four (4) bit hexadecimal (or binary) output (seee.g., FIG. 5) based on the which two of its eight (8) inputs are high.Up to this point, the device of the present invention operates like atypical DTMF receiver.

The hexadecimal output is clocked and provided to signal output unit934. In addition to being provided to the DTMF decoder 912, the outputsof the low group filter(s) 918 are provided, via comparitors 920, to afirst OR gate 950 and the outputs of the high group filter(s) 906 areprovided, via comparitors 908, to a second OR gate 952. The outputs ofthe first and second OR gates are provided to AND gate 954. The outputof the AND gate 954 is provided to a clock output enable pin of a clock926 and, via inverter 928, to the reset pin of a pulse counter 930. Thepulse train from the clock 926 is provided to the pulse counter 930.Upon being reset, the output of the pulse counter 930 is provided to aduration-to-state translation table 932.

The duration-to-state table 932 converts the duration of the dual tones,i.e., the pulse count, to an n-bit output. That n-bit output is alsoprovided to the signal output 934 which provides an (n+4)-bit outputbased on the four-bit output from the DTMF decoder 912 and on the n-bitoutput from the duration-to-state translation table 932. Thus, theduration of the dual tone signal is interpreted to provide additionalinformation.

As is further shown in FIG. 9, inverter 928′, clock 926′, pulse counter930′, and pause duration-to-state translation table 932′, may be usedinstead of, or in addition to, the aforementioned elements, forproviding n′-bits of additional information based on the duration of aninter-dual tone pause.

If the duration-to-state and/or the pause duration-to-state translationtable(s) provide an n=3-bit output, then the (n+4) or 7-bit output ofthe signal output unit 934 could be provided to an ASCII conversiontable, not shown, to convert the 7-bit signal to an ASCII value. AnASCII conversion chart is shown in FIG. 11. The ASCII conversion tablecould be provided at the central office or at the premises of an enduser.

An example of the operation of the device of the present invention willnow be provided. In the following example, is assumed that a “5” ispressed by a telephone caller for less than one second. The dual tonesequence is provided to both the high and low frequency detection units902 and 914, respectively. For the “5” digit, the high frequencydetection unit 902 will detect a 1336 Hz frequency signal exceeding athreshold amplitude, and the low frequency detection unit 914 willdetect a 770 Hz frequency signal exceeding the threshold amplitude. One(1) of the four (4) output lines of the high and low frequency detectionunits 902 and 914, respectively, corresponding to 1336 Hz and 770 Hz,will be HIGH and the other lines will be LOW.

Each of these signals output by the high and low frequency detectionunits 902 and 914, respectively, are provided to a DTMF decoder 912, thesignals output by the high frequency detection unit 902 are alsoprovided to the input of the first OR gate 952, and the signals outputby the low frequency detection unit 914 are provided to the input of thesecond OR gate 950. The DTMF decoder 912 will output a four (4) bithexadecimal number “0101”, as shown in FIG. 5, which will be provided toa first input group of the signal output unit 934. Each of the first andsecond OR gates 952 and 950, respectively, will provide a HIGH output tothe input of an AND gate 954. The AND gate will also provide a HIGHoutput to the enable pin of the clock 926 and, via inverter 928, to thereset pin of a pulse counter 930.

Since the duration of the dual frequency signal is less than one (1)second, the pulse counter 930 will only count the clock pulses duringthis time period, before it is reset. The output of the pulse counter930 is provided to the duration-to-state translation table 932. In ascheme exemplified by the grouping 650 of FIG. 6, the duration-to-statetranslation table 932 provides a one (1) bit signal of “0” to anotherinput of the signal output unit 934. In this example, the signal outputunit 934 will concatenate and output the hexadecimal output of the DTMFdecoder 912 and the n-bit signal from the duration-to-state translationtable 932; namely 00101 (i.e., “0” from the duration-to-statetranslation table 932 concatenated with “0101” from the DTMF decoder) or01010 (i.e., “0101” from the DTMF decoder concatenated with “0” from theduration-to-state translation table 932).

If, in the above example, the “5” was pressed for more than one (1)second, the duration-to-state translation table 932 would have provideda one (1) bit signal of “1” to the signal output unit 934. In thissecond example, the signal output unit 934 will concatenate and outputthe hexadecimal output of the DTMF decoder 912 and the n-bit signal fromthe duration-to-state translation table 932; namely 10101 (i.e., “1”from the duration-to-state translation table 932 concatenated with“0101” from the DTMF decoder) or 01011 (i.e., “0101” from the DTMFdecoder concatenated with “1” from the duration-to-state translationtable 932).

With the present invention, digits having duration and/or interdigitpause duration dependent information could be used by a central officeto (a) route calls and/or (b) pass information, in the form of theconcatenated output, to another central office or to an end user.Regarding the routing of calls by the central office, one telephonenumber with one or more digits of its sequence being interpreted to haveduration dependent, or interdigit pause duration dependent, information,could, for example represent one person's telephone number, facsimilenumber, pager number, e-mail number, voice mail number, etc. The presentinvention may also permit enhanced security of a PIN (or personalidentification number) having one or more digits being interpreted tohave duration dependent, or interdigit pause duration dependent,information. The invention may also be used to conserve toll freenumbers, or to avoid the need for area code changes.

The present invention is advantageous because it works with existingtelephones or other dual tone generating equipment and existingtelephone circuits. It merely requires that the DTMF receivers bereplaced or other control equipment to be reprogrammed.

The embodiments described herein are merely illustrative of theprinciples of the present invention. Various modifications may be madethereto by persons ordinarily skilled in the art, without departing fromthe scope or spirit of the invention.

What is claimed is:
 1. A method for addressing a plurality of devices ona network comprising: defining a plurality of addresses, where eachaddress is a unique sequence of two or more signals, where each signalin a respective sequence has a frequency, and at least one signal has apredetermined duration; or the sequence has a predetermined,time-specific pause between at least two adjacent signals; or at leastone signal has a predetermined duration and the sequence has apredetermined, time-specific pause between at least two adjacentsignals; and assigning one of the plurality of addresses to each device;where the combination of pause, duration, or pause and duration, withfrequency distinguishes one address from another.
 2. A method as setforth in claim 1 where the signals are DTMF.
 3. A plurality of addressesfor a plurality of devices on a network, each address comprising: aunique sequence of two or more signals assigned to a respective device,where each signal in the sequence has a frequency: and at least onesignal has a predetermined duration; or the sequence has apredetermined, time-specific pause between at least two adjacentsignals; or at least one signal has a predetermined duration and thesequence has a predetermined, time-specific pause between at least twoadjacent signals; where the combination of pause, duration, or pause andduration, with frequency distinguishes one address from another.
 4. Aplurality of addresses as set forth in claim 3 where the signals areDTMF.
 5. A code for addressing a plurality of devices on a network, thecode comprising a plurality of unique sequences of two or more signals,where each signal in a respective sequence has a frequency: and at leastone signal has a predetermined duration; or the sequence has apredetermined, time-specific pause between at least two adjacentsignals; or at least one signal has a predetermined duration and thesequence has a predetermined, time-specific pause between at least twoadjacent signals; where the combination of pause, duration, or pause andduration, with frequency distinguishes one sequence from another.
 6. Acode as set forth in claim 5 where the signals are DTMF.